Apparatus for transferring developed image

ABSTRACT

An apparatus for transferring a developed electrostatic image from an image-bearing member to a medium such as copy paper in response to the evenly distributed field produced by a D.C. biased metallized fiber brush roller which contacts the copy paper to produce the transfer.

United StatesPatent Krause et al.

1151 3,691,993 1 1 Sept. 19, 1972 APPARATUS FOR TRANSFERRING DEVELOPED IMAGE Inventors: Konrad A. Krause, Mountain View; Yaqub Moradzadeh, Saratoga, both of Calif.

International Business Machines Corporation, Armonk,

Filed: Nov. 23, 1970 Appl. No.: 92,038

Assignee:

US. Cl. ..118/637, 96/ 1.4, 1 17/ 17.5 Int. Cl. ..G03g 13/00 Field 01 Search ..118/637; 117/17.5;

101/DIG. l3; 96/l.4; 355/3 References Cited UNITED STATES PATENTS v 12/1971 Shelffo ..96/l.4

3,551,146 12/1970 Guntllach. ..96/1.4

3,152,012 10/1964 Schaffert ..118/637 3,589,895 6/1971 .Ville ..l 18/637 3,368,894 2/1968 Matkan ct a] ..1 18/637 3,328,193 6/1967 Oliphant et a1. ..118/637 2,901,374 8/1959 Gundlach ..118/637 2,959,153 11/1960 Hiden; ..118/637 3,599,605; 8/ 1971 Ralston et a1 ..118/637 Primary Examiner-Mervin Stein Assistant ExaminerLeo Millstein Attorney-Hanifin and Jancin and Otto Schmid, Jr.

[5 7] ABSTRACT An apparatus for transferring a developed electrostatic image from an image-bearing member to a medium such as copy paper in response to the evenly distributed field produced by a DC. biased metallized fiber brush roller which contacts the copy paper to produce the transfer.

8 Claims, 4 Drawing Figures BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to electrostatic image systems and more particularly to transfer of a developed image from an image-bearing member to a suitable transfer medium such as copy paper.

2. Description of the Prior Art One prior art method and apparatus for transferring a developed image to a copy sheet comprises a system wherein a corona discharge device is utilized to produce a charge on the back of the copy sheet to attract the image toner from the image forming surface to the sheet. However, any vibration of the corona wire or dirt accumulation on the corona wire causes an uneven distribution of ionization and consequently causes uneven toner transfer which is observable on the copy. The efficiency of the corona discharge device and hence the quality of the resultant image varies widely with changes in-temperature and relative humidity. In addition, when high density images are present, toner transfer by corona transfer techniques is rather inefficient. Another prior art method and apparatus for transferring a developed image utilizes a conductive roller member and a bias potential applied to the roller to produce the transfer of the developed image to the copy sheet. This method and apparatus provides satisfactory results under certain circumstances; however, the efficiency of transfer is low under certain conditions. In addition, sparking and other image distorting phenomena may occur as the copy sheet is separated from the image forming surface. It is therefore an object of this invention to produce apparatus and method for transfering a developed image comprising electrostatic charged developer particles from an image forming surface to a web of transfer material to produce a high transfer efficiency and also a consistent image under widely varying environmental conditions.

SUMMARY OF THE INVENTION The'apparatus comprises an image forming surface which may be an insulator or a photoconductive surface. An electrostatic image is produced on the surface by known techniques and the image is developed utilizing electrostatically charged developer particles which are commonly known as toner. A web of transfer material is provided adjacent to the image surface. A brush having conductive fibers is also mounted adjacent to the image surface and a constant potential difference is produced between the image surface and the brush member by means of a suitable power supply. Relative motion is procedure between the brush and the image surface so that the tips of the brush fibers move the web of transfer material into intimate contact with the image surface. The potential difference is operative to attract the toner particles comprising the developed image to the web of transfer material and due to the constant force provided by the brush fibers, substantially all of the developer particles are transferred from the image surface to the web of transfer material. The image is then fixed to the web of transfer material by any suitable technique.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of an electrophotographic apparatus embodying the present invention;

FIG. 2 is an enlarged view showing in greater detail the metallized fiber embodiment of the transfer brush means for the apparatus shown in FIG. 1.

FIG. 3 is a partial cross section view along the lines 3-3 ofFIG. lj

FIG. 4 is a schematic view of an alternate embodiment of the apparatus embodying the invention wherein a flat transfer brush means is utilized.

DESCRIPTION OF PREFERRED EMBODIMENTS One example of a particular apparatus in which the subject invention is adapted for use is the electrophotographic apparatus shown in FIG. 1. In this apparatus, a rotatable drum 10 carries around its periphery an electrophotographic photoconductive member 12 on which is directed an image which it is desired to be reproduced on the paper sheet 14. The surface of the photoconductor is uniformly charged to a predetermined polarity by corona discharge device 16. A document having the image to be copied is placed so that a suitable exposure means is operable to direct the image to expose station 18 onto the surface of the photoconductor 12. Relative motion is provided for the document at a speed synchronized with the surface speed of drum 10 in a manner known in the art. Where the photoconductive surface is illuminated by the image, the surface is discharged leaving a charged pattern in a form of the image to be copied.

Thereafter, the drum passes a development station 20 at which a toner-carrier mixture 22 is cascaded across or otherwise brought in contact with the electrostatic image on the surface of the photoconductor 12 as is known in the art. The toner, having a charge opposite from the polarity of the electrostatic image charge is attracted to the drum surface to render the image visible.

Continuing the counterclockwise rotation of the drum 10, a copy paper 14 is fed into contact with the developed electrostatic image by the rollers 24. A soft brush means 26 having resilient conductive fibers is disposed beneath the paper at the area of contact with the drum. Power supply 28 is coupled to produce a unidirectional potential between brush member 26 and the conductive backing of photoconductor 12. The potential has a polarity opposite that of the toner, thereby attracting the toner to the copy paper. After this transfer operation, the paper 14 is separated from the drum and fed past a fusing station (not shown) which serves to fuse and permanently fix the toner to the paper. Since transfer of all the image toner 29 is not usually accomplished, residual toner 30 usually remains on the drum surface after a transfer operation. The drum continues to rotate past a cleaning apparatus 32 which cleans the surface of the photoconductor and removes any excess toner. This operation completes the cycling of the drum for reproducing the desired image.

The brush member 26 comprises a plurality of unitary fibers 25 which are permanently attached to the base member 27. The fibers extend substantially outward from the base and the fibers are of substantially uniform length so that a potential applied to the brush .be produced without regard to the density of the developer particles in different portions of the developed image. The fibers are preferably of a thickness approximating the size of .the individual toner particles so that the image transfer can be accom- .plished without distortion of the image. This size fiber also eliminates damage to the'image forming surface and to the copy sheet which would result from the use of thicker and stiffer brush fibers. One suitable material is stainless steel fibers approximately 12 microns in diameter which are woven into a plush fabric which is then attached to a suitable support member. This type of brush produces excellent transfer, but is difficult to manufacture with all fibers upstanding so that a uniform field and a uniform force are produced by the brush.

' Another suitable type of brush (See FIG. 2) which is easily manufactured and produces excellent operation is a brush comprising a nonconductive fiber to which a conductive coating is applied. Brushes of synthetic materials such as dynel and rayon can be manufactured with uniformly distributed upstanding fibers on a base material. The fibers are coated with a conductive material by any suitable means to provide the desired conductivity of the fibers. In the embodimentshown in FIG. 2 of the drawings, brush means 26' comprises a base member 38 to which is fixed a plurality of uniform upstanding fibers. The fibers comprise an inner nonconductive part 40 which has an outer conductive coating 42. This construction gives control over the conductivity of the fibers so that an effective technique for the prevention of arching during separation of the image surface and the transfer material is produced.

One suitable technique for coating the surface of the fibers is the technique known in the art as electroless plating. One exampleof a brush construction utilizing this technique comprises a rayon plush fabric since this material contains a combination of physical, chemical and electrostatic properties which are suitable for this use; Other types of knit or construction such as sliver knit or flocking may be used for this purpose which results in plush fabrics with upstanding or substantially upstanding fibers. The particular fabric utilizes a double shuttle type of weave which is essential in keeping the fibers separated. The fibers are first washed and then sensitized by immersion in a suitable sensitizing solution such as stannous chloride. After sufi'icient rinsing, the fabric is then activated utilizing a suitable activating solution, for example, immersion in acidic palladium chloride solutions. After suitable rinsing, the material is placed in a proper plating bath such as a copper plating bath for a time which varies with the type of bath and the desired conductivity to be produced in the fibers. The material is then rinsed and dried. This operation produces a suitable conductive coating on the fibers so that a brush is produced by fixing the fabric to a suitable support member to produce the transfer brush. Other types of conductivecoating may be produced on the fiber surface using electroless plating, for example, nickel, cobalt, iron, etc. In these cases a trace of phosphorus usually .cod'ep'osits with the metallic layer. Precious metals such as gold, platinum and rhodium can be deposited by a double plating technique in which copper is first deposited on the synthetic fiber by the electroless plating method followed by an immersion plating technique in which all or part of copper film is converted to the desired precious metallic film. For this purpose an acidic salt solution of .precious metal is employed in which the copper plated fabric is immersed, then rinsed and dried.

Relative motion may be produced between the image forming surface and the brush means 26 by any suitable means. In the embodiment shown, drum 10 is rotated about its axis from a suitable drive motor 34 by suitable belts or gears (shown dotted in the drawings). If desired, brush means 26 may also be rotated. Brush 26 may be rotated at a speed synchronized with the drum speed or driven at a faster rate to lessen the adverse effect in the event of any separation or bunching of the fibers in brush 26. The flat brush 26" shown in FIG. 4 is maintained stationary and reliable transfer of the image is produced.

Brush 26 should maintain at least a minimum area of contact to provide good transfer. A particular apparatus utilized a flat image forming surface and a 2% inch diameter transfer brush. The brush was mohair with electroless plated copper fibers about one-eighth of an inch long. A range of potentials (700-1 ,200) and brush compressions were tried and the optimum configuration for this apparatus was found to be a potential of 1,100 volts with about 2mm compression in the brush fibers which produced a contact area approxi-v mately 1 inch wide. A 2% inch diameter stainless steel fiber brush with /4; inch fibers was also utilized. The optimum transfer current which produced good transfer without arcing was found to be 0.2[LA/ill A series resistor was used with the stainless steel fiber brush to limit the current to this level.

The invention is also applicable to other types of image producing systems other than the embodiment shown in the drawings. For example, in a system with a dielectric image bearing surface, a higher transfer potential was found to be more suitable. Potentials in the range of 1,000 to 2,000 volts were found suitable for good transfer in apparatus of this type.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in the form and details may be made therein without departing from the spirit and scope of the invention.

We claim:

1. Apparatus for transferring a developed image comprising electrostatically charged developer particles from an image forming surface to a web of transfer material comprising:

an image forming surface having a developed image thereon,

brush means having a plurality of resilient conductive fibers,

means for producing a constant potential difference between said brush means and said image forming surface, and

means for producing relative motion between the brush means and the image forming surface so that the tips of the fibers move the web of transfer material into abutting contact with said image forming surface whereby said potential is operative to transfer the developed image to said web of transfer material.

2. The apparatus according to Claim 1 wherein said brush means comprises a cylindrical base member mounted for rotation about an axis and wherein said fibers are affixed to said base member and extend substantially outward from said axis.

3. The apparatus according to claim 2 wherein said image forming surface comprises the peripheral outer surface of a drum member mounted for rotation about an axis.

4. The apparatus according to claim 3 wherein said means for producing relative motion between said brush means and said image forming means comprises means for rotating said drum and said brush means.

5. The apparatus according to claim 1 wherein said constant potential difference between said brush means and said image forming surface is between about 700 volts and 2,000 volts.

6. Apparatus for transferring a developed image comprising electrostatically charged developer particles from an image forming surface to a web of transfer material comprising:

an image forming surface having a developed image thereon,

brush means having a plurality of resilient fibers, said fibers comprising non-conductive fibers having a conductive coating thereon;

means for producing a constant potential difference between said brush means and said image forming surface; and

means for producing relative motion between the brush means and the image forming surface os that the tips of the fibers move the web of transfer material into abutting contact with said image forming surface whereby said potential is operative to transfer the developed image to said web of transfer material.

7. The apparatus according to claim 6 wherein said constant potential difference between said brush means and said image forming surface is between about 700 volts and 2,000 volts.

8. The apparatus according to claim 6 wherein said non-conductive fiber comprises synthetic material. 

1. Apparatus for transferring a developed image comprising electrostatically charged developer particles from an image forming surface to a web of transfer material comprising: an image forming surface having a developed image thereon, brush means having a plurality of resilient conductive fibers, means for producing a constant potential difference between said brush means and said image forming surface, and means for producing relative motion between the brush means and the image forming surface so that the tips of the fibers move the web of transfer material into abutting contact with said image forming surface whereby said potential is operative to transfer the developed image to said web of transfer material.
 2. The apparatus according to Claim 1 wherein said brush means comprises a cylindrical base member mounted for rotation about an axis and wherein said fibers are affixed to said base member and extend substantially outward from said axis.
 3. The apparatus according to claim 2 wherein said image forming surface comprises the peripheral outer surface of a drum member mounted for rotation about an axis.
 4. The apparatus according to claim 3 wherein said means for producing relative motion between said brush means and said image forming means comprises means for rotating said drum and said brush means.
 5. The apparatus according to claim 1 wherein said constant potential difference between said brush means and said image forming surface is between about 700 volts and 2,000 volts.
 6. Apparatus for transferring a developed image comprising electrostatically charged developer particles from an image forming surface to a web of transfer material comprising: an image forming surface having a developed image thereon, brush means having a plurality of resilient fibers, said fibers comprising non-conductive fibers having a conductive coating thereon; means for producing a constant potential difference between said brush means and said image forming surface; and means for producing relative motion between the brush means and the image forming surface os that the tips of the fibers move the web of transfer material iNto abutting contact with said image forming surface whereby said potential is operative to transfer the developed image to said web of transfer material.
 7. The apparatus according to claim 6 wherein said constant potential difference between said brush means and said image forming surface is between about 700 volts and 2,000 volts.
 8. The apparatus according to claim 6 wherein said non-conductive fiber comprises synthetic material. 